The value of local ISI calibration in correcting the variability in INR determination.

We have compared the International Normalized Radio (INR) determination using the manufactures’ stated International Sensitivity Index (ISI) with an alternative method using local calibration of ISI with the calibrator plasma. It was found that the variability of the INR was less when the results were expressed by INR using local calibration of ISI. The results indicated that the local ISI calibration might reduce the variability in the INR determination.